(1) Field of the Invention
This invention concerns an electromagnetic switching valve for switching the flowing direction of fluid by electromagnetic operation force.
(2) Description of the Prior Art
Electromagnetic switching valves known so far have generally been constituted as shown in FIG. 1, wherein a movable core 102 having a feed valve body 103 and a discharge valve body 104 is driven by ON/OFF operation of a coil 101 in a solenoid operation section on a valve main body 100, to thereby open and close a feed valve seat 105 and a discharge valve seat 106 alternately. Upon energizing, the discharge valve seat 106 communicating with a discharge port 107 is closed to establish a fluid channel from an input port 108 to an output port 109 and, upon deenergizing, the feed valve seat 105 is closed to establish a fluid channel from the output port 109 to the discharge port 107. In the electromagnetic switching valve of the type referred to above, since the resilient force of a spring 110 for actuating the feed valve body 103 is set greater than that of a return spring 111 and the movable core 102 has to be attracted, upon energizing, against a great resilient force of the return spring 111, it is necessary to employ a compact and low-priced solenoid operation section so that the solenoid be operated in a range where the electromagnetic attraction force is relatively strong, that is, it has to be used with a small stroke of the movable core. Thus, it has an inherent deficiency that the stroke of the movable core is greatly restrained and the fluid discharge performance in the feed valve seat 105 and the discharge valve seat 106 is limited significantly. If the stroke of the movable core is extended in order to increase the fluid discharge performance, the movable core has to overcome the resilient force of the return spring in weak range of the electromagnetic attraction force, which results in various defects such as increase in the size of the solenoid coil 101 or increase in the electric power consumed therein.
Further, in order to provide the feed valve seat 105 and the discharge valve seat 106 with sufficient fluid passing performance, the stroke between the feed valve body 103 and the feed valve seat 105 having a bore diameter d.sub.1 is set to 1/4d.sub.1 and, accordingly, the stroke between the discharge valve body 104 and the discharge valve seat 106 having a bore diameter d.sub.2 has to be set to 1/4d.sub.2. Therefore, if it is intended to set the bore diameter d.sub.2 greater than the bore diameter d.sub.1, that is, for increasing the discharge performance by accelerating the starting of an actuator to be controlled by the valve, the stroke of the movable core has to be set corresponding to the bore diameter d.sub.2. Accordingly, for enlarging the bore diameter d.sub.2 from the state shown in FIG. 1 in order to improve the discharge performance, the stroke of the movable core 102 must necessarily be extended. However, the machines heretofor in use are disadvantageous, in such a case, in that the distance between the two valve seats 105 and 106 has to be increased and in that such extension of the stroke, although important for the discharge valve seat 106, is quite useless and very much irrational in view of the feed valve seat 105 of a smaller bore diameter.